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Edexcel C3,C4 June 2013 Thread

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Reply 4820

username878045

Original post by Mallika

How do we find the area below the x-axis? I feel like I should know this but can't remember :frown:

Most questions ask to find the area enclosed by the curve, the x-axis and the co-ordinates!

Integration finds the total area, and area below the x-axis is considered 'negative area' therefore, if a graph has sections above and below the x-axis, you have to split it into integrals and take the modulus of the negative integral.

Reply 4821

username878045

Original post by Exotica

Here is the marking scheme for June 2005
http://www.goffs.herts.sch.uk/goffsm4/mathsalevel%20docs/pbe%20c4/2005/C4%20June%202005%20mark%20scheme.pdf
On questions 4 I'm not able to understand how they got from the first line to the second.

1 - sin²x = cos²x

(cos²x)^(3/2) = cos³x

Reply 4822

LegendX

Original post by otrivine

thank you

but how tan30=r/h :s-smilie:

Look at the attachment.

image.jpg517.4KB

Reply 4823

noeliah4

Does any1 knw how to do tht
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1371497441013.jpg31.0KB

Reply 4824

mcollin1

Original post by LastOfUs

This is an integral of the form f'(x)[f(x)]^n. This means the answer is [f(x)]^n+1/n+1. So, you can write sin^2tcost as integral of cost[sint]^2.

that kinda makes sense, but i looked in the book and its actually one of the examples, oops!

thank you :smile:

Reply 4825

mcollin1

Original post by noeliah4

Does any1 knw how to do tht
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implicit differentiation,

so differentiate x normally, and y-> dy/dx, y^2 -> 2y dy/dx etc

Reply 4826

BearOfStown

Original post by noeliah4

Does any1 knw how to do tht
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Use your dy/dx, make it equal zero and that should start you :smile:

Reply 4827

MedMed12

Original post by Fortitude

You might get an Oscar :wink:

its all about the MBE, OBEs at the moment

Reply 4828

Tikara

why is a^x differentiated a^xlnA ?

Reply 4829

otrivine

Original post by LegendX

Look at the attachment.

i see and where did root 3/3 come from?

Reply 4830

MedMed12

Original post by Tikara

why is a^x differentiated a^xlnA ?

y=a^x
lny=lna^x
lny=xlna
1/y * dy/dx = lna

dy/dx= ylna
dy/dx = a^x lna

:smile:

Reply 4831

Fiyinad

Quick Question, How do you integrate cot 3x?

Reply 4832

LegendX

Original post by Tikara

why is a^x differentiated a^xlnA ?

See attachment

image.jpg520.0KB

Reply 4833

username878045

Original post by Fiyinad

Quick Question, How do you integrate cot 3x?

cot(x) integrates to ln(sinx) - it's in the formula book.

Reply 4834

Supes180

If you swap limits by substitution and you end up with limits that have a different size order, do you still go from high to low/top to bottom? For example

\int^5_3 \ dx

turns into

\int^2_4 \ du

Is that right? Or should it be

\int^4_2 \ du

Reply 4835

LegendX

Original post by otrivine

i see and where did root 3/3 come from?

Type tan30 into your calculator and then because its h2 you must square that value

Reply 4836

Fiyinad

Original post by PythianLegume

cot(x) integrates to ln(sinx) - it's in the formula book.

Yh i get dat bit buh wah if cot3x came up in the exam? would it be 1/3ln[sin(3x)]?

Reply 4837

Fortitude

Original post by MedMed12

its all about the MBE, OBEs at the moment

Well, you see I'm living in the past so what's current for me, is the past for you & what is current for you, is in the future for me, unfortunately this does not apply to exams :tongue: